This is more of an info thread for G90 owners, I figure the more info out there the better.

I've posted my set in the f/s section as is, but I'm taking a last attempt at repairing it. THe tech in me can get pretty stubborn.

As per the f/s post, the set fires up fine, projects menu and an image, but none of the functions work, ie you can ramp any command (brightness, focus, convergence, etc) from 0 to 254, and while the onscreen numbers change, the command has no effect on the set. After about 5 minutes the set will shut down with a couple of error codes, 89 and 8A which point to the convergence boards.

I have found that one keypad command does work, the ABG control works as it's supposed to. THe gain and bias controls do nothing.

Also, right before the set shuts down with an error, the image will change in brightness, flicker slightly and on occasion the image will skew and bend slightly, as if the geometry controls change drastically. Then the set shuts down.

I've found that by disconnecting the convergence board input connectors, the set will stay on longer.

I've sent the RGB input board and the main CPU board to Terry for testing, and they check OK.

My theory so far is as follows:

1) The convergence boards are fine. I figure that the rapid changes in signal going to the convergence boards cause current spikes giving a false shutdown.

2) The waveform generator seems to do nothing, yet it gives no error codes, thus at least the power supplies feeding the waveform boards are fine.

I'm now trying to trace how the brightness and contrast adjustments are controlled. I figure the brightness and contrast controls do not go through the wave boards. Can anyone assist in the signal path here?

Disclaimer: I know absolutely nothing specifically about the Sony VPH-G90U, but since I already had the service manual open for another thread I thought I'd take a crack at this issue too.

If the YA and BA Boards were already found to work correctly in another chassis, doesn't that more or less leave only the MA Board?... Which almost narrows it down to basically a bad connector, solder joint, or trace.

The obvious suggestion would be to check around connector CN602 and CN603 (that the YA Board plugs in to) on the MA Board. Especially pins 9-10 and 12-16 on CN603, as those are the clock and data lines for the I2C Bus and Registration DACs. Somehow, given who's asking, I'm guessing it's not going to be quite that simple though, is it?

Do you get a ~5MHz (per the Theory of Operation Manual) clock waveform at CN421, Pin C12 on the YA Board?

Do you also see that same clock waveform at CN341, Pin A13 on the BA Board?

And again, let me reiterate, I may have no idea what I'm talking about... Just throwing out a few suggestions that sounded good to me at the time.

-- Ryan

Edit: A couple other things I realized...

I imagine you've already tried this, but if you input a composite NTSC signal on the video input, do the COLOR, HUE, and SHARPNESS controls work? The IC responsible for those adjustments (IC1600) is on a different bus than the DACs for BIAS, BRIGHTNESS, CONTRAST, etc. (IC609 and IC611).

Also, if the D-SCL (clock) waveform I mentioned above is present on both YA and BA boards, are you seeing periodic assertions of D-LD0 at CN421, Pin B13 (YA Board) and CN341, Pin B14 (BA Board) as well?

It _appears_ that there is no clock pulse coming out of the SCL connector. I get the 20Mhz clock going into the DAC on the CPU board, but very little is coming out of the DAC to the buffer chip. I've checked for shorts on the SCL line, and even tried feeding an external clock to the buss, but no dice.

The only thing that doesn't jive here is that I sent the CPU board to Terry and it checked fine there. This problem doesn't come and go, so it doesn't make sense that the board worked at his place and not here before it left or when it came back.

So I dunno. I've now put about 10 hours into the set, and have learned a LOT more about the G90s than I knew before I started this.

I've got several interested buyers in this set, so I'll take them in order. With luck the problem is elsewhere, and someone that already has a G90 can simply do some board swapping and then get this set running.

As a tech I hate walking away from the unit, but with no spare parts here or out there, I'll cut my losses now.

Thanks for the help on this, it was fun, if not frustrating. And my soldering station died in the middle of it, dammit!

I realize you're probably going to sell this set AS-IS, but here are a few last thoughts...

To ensure we're on the same page, when you say "DAC on the CPU board" you're referring to IC421? And you do get 20MHz at Pin 60, but nothing at TP428 (the D-SLC output)?

Anyway, a little background on my understanding (so no guarantee it's correct) of how this works:

DACs IC609 and IC611 (that control brightness, contrast, etc.) on the BA Board are loaded with data from DAC Controller IC421 on the YA Board via lines D-SLC (clock), D-SDA0 (data), and D-LD0 (load) during a 180µs period syncronized with the start of vertical retrace. The timing relationship is shown in section 17-5 of the Theory of Operation Manual. Hence, I don't think you can just inject a 5MHz square wave (if that's what you did) and expect anything (good, at least ) to happen. That clock needs to be syncronized with some other signals.

While D-SLC and D-LD0 are low, D-SDA0 is set high or low depending on the data you want loaded. D-SLC then asserts for ~100ns, loading the bit on D-SDA0 into the shift register of the DAC. That continues until all bits have been shifted in, at which point D-SDA0 and D-SLC again remain low. D-LD0 then asserts for ~200ns, which copies the data from the shift register to the selected latch register on the DAC and subsequently changes the analog output.

So, if you are seeing various pulses (you mentioned "very little") on D-SLC, D-SDA0, and D-LD0, my guess would be it's working. Even if it weren't, I'm not sure how you'd verify the data and timing are accurate without at least a two-channel storage oscilloscope.

One even simpler thing I did miss, though... Is D-RESET at CN421, Pin B12 on the YA Board high? This is connected to every DACs' Preset NOT Input which, if low, would cause them all to sit at mid-level and ignore serial input.

I've bought this Curt's G90 defective unit some time ago and did not found time to investigate it until now...

Yesterday, spent some couple of hours to swapp boards between my first 'working' G90 unit and this defective one.

I've also soldered some probing wires on the YA I²C communication links to probe all I²C lines linked to DD/DE/DF and BA boards (D-SCL, [DLD0-DLD3], [DSDA0-DSDA2] and [M1-M5] with D-Reset signal). I found that, when a failure occurs, the D-SCL signal is fading toward 0V without any reason.... Looks like a I²C bus loading problem because of a defective receiver OR a defective local power on receiver...

To investigate if it's a I²C bus loading issue, I tried to swap all DD/DE/DF boards with the one from my first unit to see if it solve the issue or not : Nothing has changed on the unit behaviour. Then, It's not these boards so not the buses loadings conditions...

Since Curt said that both YA and BA boards were checked OK by someone else, I didn't swapped those two boards yet but after checking all the PSU sections and found nothing wrong, I was wondering if is was not worth trying to swap those YA/BA boards as well, just to re-check

Then I made it yesterday and then the unit started to work fine

Found also that the green tube bad G1/G2 bias (ABL ?) I had was due to the BA board (this failure disappeared with my working BA board)

- Then, I must conclude that the I²C buses failure is relevant to YA board ONLY.
- The Green tube overdrive issue is only relevant to BA board .

I will try to change IC13 (74HCT541 SOIC20 chip) I²C bus buffer on YA board and probe the Green channel after IC404 (LM1283) device since the green overdrive is present with internal tests patterns on BA board.

Curt, did you noticed that green tube was overdriven when you've investigate the unit ?

Is there any "protection zeners" parallel in those sda/scl lines..I remember time ago(maybe 10 years) when sony car radios did get "nuts". sometimes those prot.zeners was leaky and they maked little shorts and prosessor think that was data... Some macines turned on and pumped volume up etc...
And solution was to chance all prot zeners on those lines ( bad component batch)

John, glad you're making progress! No, I never saw the green tube being overdriven, when I did get a pix out of it, it seemed relatively normal for the few minutes that it did run..

I'll check my notes, but I think I sent Terry Ferentinos the Ya board along with others to test, and he said all of the boards I sent him tested OK. But if it's intermittent for you, then I guess that's what happened.

If it is intermittent though, I'd suspect a bad solder joint on an SMT chip. Unless you find otherwise, chips themselves ususally don't go intermittent. Barcos are really bad for bad connections on the SMT leads of chips.

As mentioned earlier, there's a leaky diode (esd) on one of the data lines. That leaky diode will hold down data transmission causing some functions to not work at all, and will also cause intermittent operation.

It can be hell to track down, but it's a very common data problem on a lot of Sony broadcast gear, as well some other stuff.

As mentioned earlier, there's a leaky diode (esd) on one of the data lines. That leaky diode will hold down data transmission causing some functions to not work at all, and will also cause intermittent operation.

It can be hell to track down, but it's a very common data problem on a lot of Sony broadcast gear, as well some other stuff.

In fact the issues are not intermittent at all. Then I don't think this can be a solder on boards. I rather suspect something wrong with the YA board I²C lines drivers chips (HCT541) but I do have difficulties to find this part with 20 pins narrow body shape (only wide)

About diode, yes that can be a reason if there is such diodes on the I²C lines, but as far as I know (I will check again ), Sony did not use ESD protection diodes on these communications lines ...

I know this is simplistic, but I discovered that one of the major problems with my G90 was board sag. In particular, the YA and power boards in the back of the set were sagging and shorting out. I propped them up with a small piece of plastic, and solved most of my problems.
Just a note for posterity. E.

Spent some time on the G90 Service manual and didn't see any diodes on the SPI/I²C lines between YA and BA/DD/DE/DF boards. I only seen 100R serial resistors in front of each receivers ICs SDA/SCL inputs on BA/DD/DE/DF schematics.

Ed, Thanks for the tip but checked this when I did cleanup all the G90 unit boards.

Spent some time on probing BA (4/12 schematic) RGB BKG CONTROL section to compare analog signals between Green (defective) and Red/Blue (OK). Found that BKG-G output signal was too low (1.32V) instead of ~3V.

- Tried to change IC601 (MUX) and IC604 (Current to voltage converter) : no fix .
- Spent one hour with removed BA board on impedance probing around IC601 vs IC600 and IC602 : found that IC601 pin#1 impedance vs +12V rail was 10K higher than the two others chips
- I then usoldered R603 (100K 0.5% SMD0805) and check it with ohmmeter : found it opened
- Tried a new 100K SMD0805 resistor in replacement, plugged back BA board on G90 and fire : works fine now

BA board failure solved

I never saw such open resistor like this on board in my all EE life
Let's repair the YA then !

John, have you tested those "tv-serviceman´s trouble finding routines" hairdryer & coldspray??and are you taked good look at those smd elyt.caps, many times leaky caps..Forget! you know this stuff allready